Inorganic materials mainly composed of a compound semiconductor having fluorescence emission properties have been used as a light-emitting material and a photo-storage material. In recent years, light-emitting materials having electroluminescence (EL) properties and being capable of emitting light with electric energy are expected as a novel material for light emitting elements used in light sources or display apparatuses and have attracted attention. However, most of currently available inorganic EL materials are inadequate in efficiency of converting electric energy into light, and have a problem of heat generation and also problems with power consumption, EL brightness and the like. Thus, research and development have been conducted in search of a more practical inorganic EL material.
For example, in connection with development of blue EL materials, research has been conducted on methods for producing a phosphor comprising zinc sulfide as a host.
It is known as one approach for producing a zinc sulfide based phosphor to thermally dope a luminescent center into a zinc sulfide host (refer to, for example, Patent Document 1). Another known approach for producing a zinc sulfide based phosphor comprises doping a zinc sulfide with a luminescent center while the zinc sulfide is chemically produced. In the latter approach, a metal salt containing a metal element that acts as a luminescent center may be combined with a zinc salt before producing zinc sulfide under hydrothermal conditions (refer to, for example, Patent Document 2), or alternatively, an aqueous solution of a sulfurizing agent may be added to react with a liquid solution containing a zinc salt and metal salts, wherein said metal salts comprise a metal element that acts as a luminescent center (refer to, for example, Patent Document 3). Patent Documents 2 and 3 describe that a phosphor precursor thus obtained is heated and fired to cause immobilization of luminescent center and crystallization, which provide in conversion of the phosphor precursor into a phosphor.